Mixture adaptation method for internal combustion engines with direct gasoline injection

ABSTRACT

A method for compensating for faulty adaptations of the pilot control of fuel metering for an internal combustion engine which is operated in the at least two different operating modes, homogeneous mode and stratified charge mode. The method includes mixture regulation and adaptation of mixture regulation occurring in homogeneous mode; switching occurring between the operating modes, depending on a desired operating mode which is determined from a plurality of operating mode requirements. Furthermore, each of the operating mode requirements are assigned a priority; and the desired operating mode is determined depending on the priorities of the operating mode requirements. Also, switching to homogeneous mode with the activation of the adaptation momentarily occurs, even outside the normal starting conditions of the adaptation. A deviation of the adaptation quantity from its neutral value during the short-time activation is evaluated as a suspected error, with the engine control program elevating the priority of the adaptation under normal starting conditions when a suspected error is present.

FIELD OF THE INVENTION

The present invention relates to method of adapting mixtures forinternal combustion engines having direct gasoline injection.

BACKGROUND INFORMATION

It is conventional in the regulation of the fuel/air ratio of internalcombustion engines to superimpose a pilot control including aregulation. It is further conventional that additional correctingquantities may be derived from the behavior of the regulating quantityto compensate for faulty adaptations of the pilot control to modifiedoperating conditions. This compensation is also referred to asadaptation. U.S. Pat. No. 4,584,982 describes, for example, anadaptation with different adaptation quantities in various ranges of theload/speed spectrum of an internal combustion engine (range adaptation).The various adaptation quantities are directed toward compensation fordifferent errors. Three types of errors may be distinguished, accordingto their cause and effect: errors of a hot film air flow sensor, whichhave a multiplicative effect on the fuel metering; air leakageinfluences, which have an additive effect per unit of time; and errorsin the compensation of pickup delays of injection valves, which have anadditive effect per injection.

Under regulatory requirements, errors pertaining to exhaust gasemissions must be detected by an onboard arrangement, optionally withthe activation of a malfunction light. Mixture adaptation is also usedfor fault diagnosis. An error is indicated if, for example, thecorrective intervention of the adaptation is too great.

Over the operating life, for the manufacturing tolerance and duringunregulated sensor heating, the measured lambda value deviates from thelambda value which is physically present, primarily in the stratifiedcharge mode in engines having direct gasoline injection.

Since the mixture adaptation takes the measured lambda into account forerror learning, the adaptation in stratified charge mode does not leadto the desired result. For the adaptation, therefore, the operation isswitched to homogeneous mode and mixture adaptation is activated.

An engine control program is described in German Published PatentApplication No. 198 50 586 which controls switching between stratifiedcharge mode and homogeneous mode.

In stratified charge mode, the engine is operated with a highlystratified cylinder charge and high excess air to obtain the lowestpossible fuel consumption. The stratified charge is achieved by delayedfuel injection, which ideally results in a division of the combustionchamber into two zones, with the first zone containing a combustibleair-fuel cloud mixture at the spark plug. The first zone is surroundedby the second zone which includes an insulating layer composed of airand residual gas. Consumption may be optimized by operating the enginelargely unthrottled while avoiding charge exchange losses. Thestratified charge mode may be preferred at comparatively low load.

At higher load, when optimization of performance is of chief importance,the engine is operated with homogeneous cylinder filling. Homogeneouscylinder filling results from early fuel injection during the intakeprocess. Consequently, there is more time for forming a mixture up tothe point of combustion. Performance may be optimized in this mode ofoperation, for example, by making use of the entire volume of thecombustion chamber for filling with the combustible mixture.

Several starting conditions are necessary with regard to adaptation:

For example, the engine temperature must have reached the startingtemperature threshold, and the lambda sensor must be ready to operate.In addition, the current values of load and rotational speed must bearranged in specific ranges in which learning occurs. This is describedin U.S. Pat. No. 4,584,982, for example. Furthermore, the operation mustbe in homogeneous mode. According to the conventional program, theswitching from stratified charge mode to homogeneous mode is independentof whether an error is present in the system.

SUMMARY

It is an object of the present invention to increase the time period inwhich the engine is capable of being operated in stratified charge modewith optimum consumption. Switching to homogeneous mode for diagnosismay reduce the consumption-related advantages of direct gasolineinjection, since homogeneous mode may be more unfavorable forconsumption than stratified charge mode. Switching to homogeneous modetherefore may unnecessarily increase the fuel consumption when an erroris not present. Switching to homogeneous mode may thus be avoided to thegreatest extent possible without compromising the detection of exhaustgas-related errors.

A method is described to compensate for faulty adaptations of the pilotcontrol of fuel metering (adaptation) for an internal combustion enginewhich is operated in the at least two different operating modes,homogeneous mode and stratified charge mode, with mixture regulation andadaptation of mixture regulation occurring in homogeneous mode, withswitching occurring between the operating modes, as a function of adesired operating mode which is determined from a plurality of operatingmode requirements, each of the operating mode requirements beingassigned a priority, with the desired operating mode being determineddepending on the priorities of the operating mode requirements, withswitching to homogeneous mode with the activation of atemperature-dependent adaptation momentarily occurring, even outside thenormal starting conditions of a range-dependent adaptation, and with adeviation of the magnitude of adaptation from its neutral value duringthe short-time activation of the temperature-dependent adaptation beingevaluated as a suspected error, and with the engine control programraising the priority of the range-dependent adaptation under normalstarting conditions when a suspected error is present.

An example embodiment may provide that the short-time mixture adaptationis activated below the minimum temperature of the range-dependentadaptation.

A further example embodiment may provide that the minimum temperature ofthe range-dependent adaptation is equal to or greater than 70° C.

A further example embodiment may provide that the short-time mixtureadaptation is activated for a period of time in the range ofapproximately 10 to 20 seconds.

A further example embodiment may provide that the physical priority iscanceled if the error has been learned in the normal range-dependentmixture adaptation, so that the range-dependent mixture adaptation isenabled at normal priority by the engine control program.

A further example embodiment may provide that the value of thetemperature-dependent short-time adaptation is maintained when the motorvehicle is parked, and during the initialization phase, after the nexttime the engine is started, it is set back by the value learned withinthe scope of normal range-dependent mixture adaptation.

A further example embodiment may provide that the operatingparameter-dependent (range-dependent) mixture adaptation has amultiplicative and/or additive effect on the fuel metering.

A further example embodiment may provide that the value or values of therange-dependent adaptation are renewed above a temperature threshold andhave an effect on the fuel metering independent of temperature.

A further example embodiment may provide that the deviation of theinstantaneous temperature-dependent adaptation factor is derived from along-term adaptation factor to form the suspected error.

The present invention is also based on an electronic control device forperforming at least one of the aforementioned methods and exampleembodiments.

One aspect of the present invention is a short-time mixture adaptationwhich occurs even outside the normal starting conditions of theadaptation, e.g., below the minimum temperature of the range-dependentadaptation. According to the present invention, the short-time mixtureadaptation is activated only for a very short period of time, in therange of approximately 10 to 20 seconds. If an error is present, themagnitude of the correction of the short-time temperature-dependentadaptation deviates from its neutral value.

According to the present invention, the deviation raises the priority ofthe normal mixture adaptation within the scope of the operating modecontrol program. If the operating conditions of the normal mixtureadaptation are then satisfied, the normal mixture adaptation is startedrelatively quickly.

If the error has been learned in the normal range-dependent mixtureadaptation, the physical priority is canceled, with the result that therange-dependent mixture adaptation operates only when it is enabled atnormal priority by the engine control program.

Since the value of the temperature-dependent short-time adaptation ismaintained when the motor vehicle is parked, and is incorrect the nexttime the engine is started, again in the de-adapted state, thetemperature-dependent short-time adaptation is set back during theinitialization phase, after the next time the engine is started, by thevalue learned within the scope of normal range-dependent mixtureadaptation.

This may provide the advantage that in the non-adapted state thephysical priority of the normal adaptation immediately increases.

Since the temperature-dependent adaptation may provide only a 3 to 4%correction in the normal state, the maximum of the integrator iscorrected downward or upward, depending on the learned error, so that,for example, for a 20% error learned only a 5% correction is permitted.

In the error-free state, switching to homogeneous mode occurs only inlarge time intervals. In the error state of a cold engine, the timeintervals during the operation are at first very short, and then long.If no error has been learned, the short time intervals are repeatedafter the engine starts. If an error is learned, operation occurs inhomogeneous mode, once again in long time intervals. In the methodaccording to the present invention, switching to homogeneous mode, whichmay be less favorable for consumption, is performed only very briefly,and for suspected errors, the temperature-dependent mixture adaptationis activated immediately. If no error is present in the system, themixture adaptation is activated less frequently, so that the time periodin which the engine is capable of being operated in stratified chargemode with optimal consumption is extended.

An example embodiment of the present invention is explained hereinafterwith reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the technical field of the present invention.

FIG. 2 illustrates the formation of a fuel metering signal based on thesignals illustrated in FIG. 1.

FIG. 3 illustrates the formation of a temperature-dependent adaptationquantity as used in the present invention.

FIG. 4 represents an example embodiment of the present invention in theform of function blocks.

DETAILED DESCRIPTION

As illustrated in FIG. 1, an internal combustion engine 1 includes anintake pipe 2, an exhaust pipe 3, fuel metering arrangement 4, sensors 5through 8 for operating parameters of the engine, and a control device9. Fuel metering arrangement 4 may include, for example, an arrangementof injectors for direct injection of fuel into the combustion chambersof the internal combustion engine.

Sensor 5 sends a signal to the control device via air flow ml which isdrawn in by the engine. Sensor 6 sends an engine speed signal n. Sensor7 may provide information on the engine temperature T, and sensor 8sends a signal Us indicating the engine exhaust gas composition. Fromthese and optionally additional signals regarding other engine operatingparameters, the control device forms, in addition to other controlvariables, fuel metering signals ti to actuate fuel metering arrangement4 in such a manner that a desired engine response, e.g., a desiredexhaust gas composition, may be established.

FIG. 2 illustrates the formation of the fuel metering signal. Block 2.1represents a characteristic field which is addressed by rotational speedn and relative air filling rl, and in which pilot control values rk forthe formation of fuel metering signals are recorded. Relative airfilling rl is based on a maximum filling of the combustion chamber withair, thereby indicating to a certain extent the fraction of maximumfilling of the combustion chamber or cylinder. Relative air filling rlis based essentially on signal ml. rk corresponds to the quantity offuel which is allocated to quantity of air rl.

Block 2.2 illustrates the multiplicative lambda regulation intervention.A faulty adaptation of the quantity of fuel to the quantity of air isindicated by signal Us from the exhaust probe. From signal Us aregulator 2.3 forms regulating quantity fr which reduces the faultyadaptation by intervention 2.2.

The metering signal, for example, an actuation pulse duration for theinjection valves, may be formed in block 2.4 from the signal thuscorrected. Thus, block 2.4 represents the conversion of the relative andcorrected quantities of fuel into a real actuation signal, taking thefuel pressure, injection valve geometry, etc., into account.

Blocks 2.5 through 2.9 represent the operating parameter-dependent(range-dependent) mixture adaptation, which may have a multiplicativeand/or additive effect. Circle 2.9 represents these three possibilities.Switch 2.5 is opened or closed by arrangement 2.6, which is suppliedwith operating parameters of the internal combustion engine such astemperature T, air flow ml, and rotational speed n. Arrangement 2.6 inconjunction with switch 2.5 thus may allow the three referencedadaptation possibilities to be activated, depending on the operatingparameter range. The formation of adaptation intervention fra onto thefuel metering signal formation is illustrated by blocks 2.7 and 2.8.When switch 2.5 is closed, block 2.7 forms average value frm ofregulating quantity fr. Deviations of average value frm from the neutralvalue 1 are taken by block 2.8 into adaptation intervention quantityfra. For example, if regulating quantity fr first goes to 1.05 as theresult of a faulty adaptation of the pilot control, the deviation of0.05 from the value 1 is taken by block 2.8 into value fra of theadaptation intervention. For a multiplicative fra intervention, fra thengoes to 1.05, with the result that fr returns to 1. The adaptation thusassures that faulty adaptations of the pilot control need not bereadjusted for every change in the operating point. This adjustment ofadaptation quantity fra is performed at high temperatures in theinternal combustion engine, such as above a cooling water temperature of70° C., with switch 2.5 at that time being in the closed state. Onceadjusted, however, fra affects the formation of the fuel metering signaleven when switch 2.5 is open.

This adaptation is supplemented within the scope of the presentinvention by additional correction frat, which acts in gate 2.10.

FIG. 3 represents an example embodiment of frat formation. Block 3.1sends the deviation of average manipulated control variable frm from thevalue 1 to an integrator block 3.2. Block 3.3 activates the integratorfor comparatively low engine temperatures T in an interval TMN<T<TMX. Asthe lower interval limit, TMN may be 20° C., for example; as the upperinterval limit, TMX may correspond, for example, to the temperature atwhich customary adaptation is activated by closing switch 2.5. A typicalvalue for this temperature is 70° C.

With value frak, the starting value of the integrator gives a measure ofthe faulty adaptation in a comparatively cold engine.

This value is taken into account during formation of the fuel meteringsignal in a cold engine without causing differences from the adaptationin a warm engine at high temperatures.

This is achieved, for example, by blocks 3.4 through 3.6 and 2.10.

Gating of integrator output frak with a temperature-dependent quantityftk may be essential in this context. In the example, ftk represents amultiplicative correction which varies between zero and one. The valuezero is obtained for a warm engine, that is, where T>TMX. The minimumselection in block 3.7 then sends value TMX. The value zero is obtainedin block 3.8 as the difference between TMX and TMX, and is sent toquotient formation in block 3.9 as a numerator. Block 3.8correspondingly sends the value zero for the quantity oftemperature-dependent quantity ftk. The value 1 is added to this valueftk=0 in block 3.6. Sum frat accordingly has the value 1, and during themultiplicative gating in block 2.10 it does not change the formation ofthe fuel metering signal for a warm engine. That is, for a warm engine,ftk has a maximum weakening effect on frak. For a cold engine at T=0°C., for example, the minimum selection sends the value zero, and thesubsequent quotient formation sends the value 1. ftk is then neutral,and has a minimum weakening effect or no weakening effect on frak. Tocompensate for the addition of 1 in block 3.6 in this case, 1 issubtracted in block 3.4. For a cold engine (T=0), frak accordingly hasan effect (frak−1)*1+1=frak on the formation of the fuel metering signalwhich is unchanged and therefore not weakened. In other words, thefurther adaptive (temperature-dependent) correction functions only for acold engine. The correction constantly varies between the referencedextreme values.

Characteristic map 3.10 sends values K for the integration rate inintegrator 3.2, depending on the values for drl and n. Thus, forexample, the smaller the value of K, the larger the value of drl. drl isthe change in the air mass drawn in, which is large in transitionaloperating states, for example. In this manner, faulty adaptations affectthe adaptation only in a weakened form in transitional operating states.

frm, the deviation from one, is multiplied by factor ftk since theengine temperature is changed and value frak, which is learned in theintegrator, should be independent of temperature.

FIG. 4 represents an example embodiment of the present invention in theform of function blocks.

Block 4.1 represents the formation of quantities frat and frakillustrated in FIG. 3. To form the suspected error, first a long-termadaptation factor fratia is formed in the range of thetemperature-dependent mixture adaptation (block 4.2). To a certainextent this is the portion of cold adaptation factor frak, which alwaysappears when the engine is cold. Although a similar value, 2.5%, forexample, may always appear in the error-free state duringtemperature-dependent adaptation, this value does not indicate an error.This constantly appearing value is stored in the control device.

Furthermore, to form the suspected error, the deviation of theinstantaneous temperature-dependent adaptation factor frak fromlong-term adaptation factor fratia is derived as follows:

dfrat=absolute value (frak−fratia)

The formation of the differential and absolute values is represented byblocks 4.3 and 4.4, respectively. dfrat is then compared to suspectederror threshold FVLRAS (block 4.5). If this threshold is exceeded,condition B-fvlra is set in block 4.6 by a flip-flop. The suspectederror corresponds to a high priority for the normal adaptation whichoccurs when the engine is warm. On account of the high priority whichhas resulted from setting the established suspected error within thescope of the short-time temperature-dependent adaptation, switching tohomogeneous mode is then accelerated and normal mixture adaptation isactivated (block 4.7) as soon as the remaining starting conditions forthe normal mixture adaptation are present.

What is claimed is:
 1. A method for compensating for faulty adaptationsof the pilot control of fuel metering for an internal combustion engineoperated in at least two different operating modes including ahomogeneous mode and a stratified charge mode, comprising the steps of:performing a mixture regulation and an adaptation of mixture regulationin the homogeneous mode; switching between the operating modes dependingon a desired operating mode determined from a plurality of operatingmode requirements; assigning a priority to each of the operating moderequirements; determining the desired operating mode depending on thepriorities of the operating mode requirements; switching to thehomogeneous mode with an activation of a temperature-dependentadaptation momentarily occurring even outside normal starting conditionsof a range-dependent adaptation; evaluating a deviation of atemperature-dependent adaptation quantity from a neutral value during ashort-time activation as a suspected error; and raising, by an enginecontrol program, the priority of the adaptation under normal startingconditions when the suspected error is present.
 2. The method accordingto claim 1, further comprising the step of activating the short-timemixture adaptation below a minimum temperature of the range-dependentadaptation.
 3. The method according to claim 2, wherein the minimumtemperature of the range-dependent adaptation is greater than or equalto 70° C.
 4. The method according to claim 1, further comprising thestep of activating the short-time mixture adaptation is activated for aperiod of time in the range of approximately 10 to 20 seconds.
 5. Themethod according to claim 1, further comprising the step of canceling aphysical priority if the error has been learned in a normalrange-dependent mixture adaptation, so that the range-dependent mixtureadaptation is enabled at normal priority by the engine control program.6. The method according to claim 1, further comprising the steps of:maintaining a value of the temperature-dependent short-time adaptationwhen a motor vehicle is parked; and during an initialization phase,after a next time the engine is started, setting the value of thetemperature-dependent short-time adaptation back by a value learnedwithin the scope of a normal range-dependent mixture adaptation.
 7. Themethod according to claim 1, wherein an operating parameter-dependentmixture adaptation includes at least one of a multiplicative and anadditive effect on fuel metering.
 8. The method according to claim 1,further comprising the step of renewing at least one value of therange-dependent adaptation above a temperature threshold, the at leastone value having an effect on fuel metering independently oftemperature.
 9. The method according to claim 1, further comprising thestep of deriving a deviation of a current temperature-dependentadaptation factor from a long-term adaptation factor to form thesuspected error.
 10. An electronic control device configured to performa method for compensating for faulty adaptations of the pilot control offuel metering for an internal combustion engine operated in at least twodifferent operating modes including a homogeneous mode and a stratifiedcharge mode, the method including the steps of: performing a mixtureregulation and an adaptation of mixture regulation in the homogeneousmode; switching between the operating modes depending on a desiredoperating mode determined from a plurality of operating moderequirements; assigning a priority to each of the operating moderequirements; determining the desired operating mode depending on thepriorities of the operating mode requirements; switching to thehomogeneous mode with an activation of a temperature-dependentadaptation momentarily occurring even outside normal starting conditionsof a range-dependent adaptation; evaluating a deviation of atemperature-dependent adaptation quantity from a neutral value during ashort-time activation as a suspected error; and raising, by an enginecontrol program, the priority of the adaptation under normal startingconditions when the suspected error is present.
 11. The device accordingto claim 10, wherein the method further includes the step of activatingthe short-time mixture adaptation below a minimum temperature of therange-dependent adaptation.
 12. The device according to claim 11,wherein the minimum temperature of the range-dependent adaptation isgreater than or equal to 70° C.
 13. The device according to claim 10,wherein the method further includes the step of activating theshort-time mixture adaptation is activated for a period of time in therange of approximately 10 to 20 seconds.
 14. The device according toclaim 10, wherein the method further includes the step of canceling aphysical priority if the error has been learned in a normalrange-dependent mixture adaptation, so that the range-dependent mixtureadaptation is enabled at normal priority by the engine control program.15. The device according to claim 10, wherein the method furtherincludes the steps of: maintaining a value of the temperature-dependentshort-time adaptation when a motor vehicle is parked; and during aninitialization phase, after a next time the engine is started, settingthe value of the temperature-dependent short-time adaptation back by avalue learned within the scope of a normal range-dependent mixtureadaptation.
 16. The device according to claim 10, wherein an operatingparameter-dependent mixture adaptation includes at least one of amultiplicative and an additive effect on fuel metering.
 17. The deviceaccording to claim 10, wherein the method further includes the step ofrenewing at least one value of the range-dependent adaptation above atemperature threshold, the at least one value having an effect on fuelmetering independently of temperature.
 18. The device according to claim10, wherein the method further includes the step of deriving a deviationof a current temperature-dependent adaptation factor from a long-termadaptation factor to form the suspected error.